Device and method for detecting overlay error

Abstract

A device including a light source, illumination system, objective lens, and detector. The light source produces measurement light beams, the illumination system directs measurement light beams into the objective lens, and the objective lens directs measurement light beams onto an overlay marker, collects main maximums of diffracted light beam diffracted from the overlay marker, and focuses main maximums of diffracted light beam onto a pupil plane of the objective lens. The detector is positioned on the pupil plane of the objective lens and used for detecting the position of each main maximums of diffracted light beam on the detector, to obtain the overlay error of said overlay marker. Diffracted-light position information is used to measure overlay error, and measurement signals are not affected by illumination uniformity, transmissivity uniformity, etc.

What is claimed is: 
     
       1. An apparatus for overlay error detection, comprising a light source, an illumination system, an objective lens and a detector, wherein: the light source is configured to produce a measuring light; the illumination system is configured to make the measuring light incident on the objective lens; the objective lens is configured to direct the measuring light onto an overlay mark, collect main maximums of diffracted light components diffracted from the overlay mark and converge the main maximums of the diffracted light components onto a pupil plane of the objective lens; and the detector is arranged on the pupil plane of the objective lens and configured to measure positions of the main maximums of the diffracted light components on the detector and obtain an overlay error of the overlay mark based on a dependence of the positions of the main maximums of the diffracted light components on the pupil plane of the objective lens on the overlay error,
 wherein a number of pitches in the overlay mark is less than 20. 
 
     
     
       2. The apparatus for overlay error detection according to  claim 1 , wherein the illumination system comprises a collimator lens, a filter, a first lens, a field stop, a second lens and a splitter, disposed sequentially in a direction of propagation of the measuring light. 
     
     
       3. The apparatus for overlay error detection according to  claim 2 , wherein the illumination system further comprises a polarizer disposed between the filter and the first lens. 
     
     
       4. The apparatus for overlay error detection according to  claim 2 , wherein the illumination system comprises an aperture stop disposed between the filter and the first lens, and wherein the aperture stop is implemented as a circular hole or a slit. 
     
     
       5. The apparatus for overlay error detection according to  claim 4 , wherein two circular holes or two slits are provided, and wherein the two circular holes or slits are symmetric to each other with respect to a center of the aperture stop. 
     
     
       6. The apparatus for overlay error detection according to  claim 4 , wherein at least three circular holes or slits are provided. 
     
     
       7. The apparatus for overlay error detection according to  claim 1 , wherein the overlay mark has a size less than or equal to 10 μm*10 μm. 
     
     
       8. The apparatus for overlay error detection according to  claim 1 , wherein the main maximums of the diffracted light components are of plus and minus first orders. 
     
     
       9. The apparatus for overlay error detection according to  claim 1 , wherein the overlay mark consists of two stacked gratings formed in a substrate. 
     
     
       10. A method for overlay error detection using the apparatus for overlay error detection as defined in  claim 1 , wherein: a light source produces a measuring light; an illumination system makes the measuring light incident on an objective lens; the objective lens directs the measuring light onto an overlay mark, collects main maximums of diffracted light components diffracted from the overlay mark and converges the main maximums of the diffracted light components onto a pupil plane of the objective lens; and a detector arranged on the pupil plane of the objective lens measures positions of the main maximums of the diffracted light components on the detector and obtains an overlay error of the overlay mark based on a dependence of the positions of the main maximums of the diffracted light components on the pupil plane of the objective lens on the overlay error,
 wherein a number of pitches in the overlay mark is less than 20. 
 
     
     
       11. The method for overlay error detection according to  claim 10 , wherein the overlay mark has a size less than or equal to 10 μm*10 μm. 
     
     
       12. The method for overlay error detection according to  claim 10 , wherein the illumination system comprises an aperture stop which is implemented as a circular hole or a slit. 
     
     
       13. The method for overlay error detection according to  claim 12 , wherein two circular holes or two slits are provided, and wherein the two circular holes or slits are symmetric to each other with respect to a center of the aperture stop. 
     
     
       14. The method for overlay error detection according to  claim 12 , wherein at least three circular holes or slits are provided. 
     
     
       15. The method for overlay error detection according to  claim 10 , wherein the main maximums of the diffracted light components are of plus and minus first orders. 
     
     
       16. The method for overlay error detection according to  claim 10 , wherein the overlay error is obtained by performing a linear fitting on the positions of the main maximums of the diffracted light components on the detector.